Helium isotopic compositions in fluid inclusions of the Gangxi fault belt in the Huanghua Depression, Bohai Bay Basin

The authors obtained 30 core samples from 15 wells in Gangxi fault belt, Huanghua Depression. Using a VG5400 mass spectrometer, the helium isotopic compositions in fluid inclusion of these samples were analysed. Interpretation of results suggests a significant amount of mantle-derived helium in the inclusions, which were likely trapped during Neocene. Mantle-derived helium have mostly accumulated in the intersections of the NWW trending Xuzhuangzi and NE trending Gangxi faults, and decreased away from the intersections. This pattern implied a close relationship to the local tectonic setting. Gangxi fault belt experienced intensive neo-tectonic activities in the Cenozoic. Widespread faulted-depressions and strong volcanic eruptions manifested its tectonic status of extensional stress field. Mantle uplift caused the movement of magma that carried mantle-derived gas, and the deep-rooted tension faults provided the passages for the gases to shallow crust levels. High-content abiogenic CO2 pools occurred in the study area, hence, using the helium isotopic compositions is of great significance to the exploration of abiogenic natural gases.